1. Field of the Invention
The present invention relates to a power supply device that is connected to at least two electric power sources and that outputs a DC voltage. The present invention also relates to a construction machine to which this power supply device is mounted.
2. Description of Related Art
A battery driven construction machine is known from the prior art. In Patent Document #1, there is described a construction machine that employs an electric motor as a drive power source, and whose power supply unit can be connected either to a three phase power supply grid or to a high voltage battery. The three phase voltage from the three phase power supply grid is supplied via an AC/DC converter to an inverter of the electric motor, while on the other hand the DC voltage from the high voltage battery is used, just as it is, as a drive voltage for the inverter.    Patent Document #1: Japanese Laid-Open Patent Publication No. 2007-228715.
This type of power supply unit has the advantage that it is not subject to constraints upon its range of utilization, since it can selectively utilize either an AC power supply grid or an internal battery. However it suffers from the inconveniences that a three phase AC power supply is essential, since with a single phase household power supply the electrical current becomes too great, and moreover that a high voltage battery is essential in order to match the drive voltage of the inverter. Furthermore there is the problem that it is not possible to charge such a high voltage battery from an AC power supply grid that is at low voltage, unless a boosting chopper circuit or the like is provided separately.